Methods of Optimizing Vehicular Air Conditioning Control Systems

ABSTRACT

Air conditioning system controls are optimized for an air conditioning system having a compressor in IC engine vehicles and in hybrid or fuel cell vehicles having electric drive motors by first determining the operating temperature of at least one of the following vehicle components: engine coolant and transmission oil for all types of vehicles, and for hybrid or fuel cell vehicles also determining the operating temperature of inverter coolant and the electric drive motors. At least one operating temperature is then compared to lower and upper temperature limits. If the operating temperature is outside of the temperature limits air conditioner heat load is reduced by at least one of the following steps: increasing cabin air recirculation, reducing cabin blower speed and reducing air conditioner compressor capacity. Subsequent to reducing air conditioner heat load, selected operating temperature or temperatures are monitored to determine if the operating temperature exceeds the upper temperature limit or limits. If the operating temperature or temperatures exceed the upper limit or limits the compressor is shut off.

FIELD OF THE INVENTION

The present invention is directed to methods of optimizing vehicular airconditioning control systems. More particularly, the present inventionis directed to such methods which result in reduced propulsion coolingsystem size in non-hybrid vehicles and lower operating temperature forcoolant loops in hybrid and fuel cell vehicles.

BACKGROUND OF THE INVENTION

Conventional vehicle propulsion cooling systems include heat exchangersand fans, the size of which is based on propulsion system losses. Lossesare absorbed by engine coolant, engine oil and transmission oil. Thoselosses typically are momentarily exacerbated when the vehicle operateson a steep gradient and/or is towing a trailer, especially when theambient air temperature is high. With respect to hybrid and fuel cellvehicles, propulsion cooling loops require lower operating temperaturesthan conventional power train vehicles.

Air conditioning condensers are typically the first heat exchangers inthe CRFM (Condenser Radiator Fan Module) air stream. Propulsion coolingsystem heat exchangers typically include engine radiators andtransmission oil coolers. Hybrid and fuel cell vehicles also includeinverter radiators and electric motor radiators. These heat exchangersare typically disposed downstream of the A/C (Air Conditioning)condenser, and are therefore affected by A/C condenser heat load.

In current production vehicles having power train controls, whenpropulsion cooling systems approach maximum temperature limits, A/Csystem control is typically limited to A/C compressor interrupt. A/Ccompressor interrupt results in a complete loss of cabin cooling becausethe A/C system simply shuts off when propulsion system thermal limitsare reached.

SUMMARY OF THE INVENTION

In view of the aforementioned considerations, the present inventionoptimizes air conditioning systems for vehicles by momentarily reducingA/C condenser heat load during transient, high ambient temperature/highpropulsion system load events, thereby allowing an overall reduction inpropulsion cooling system size.

Reducing the required propulsion cooling system size includes at leastone of the following possibilities:

1) reducing radiator cooling size, e.g., by core thickness reduction,fin density reduction, and/or core face area reduction;

2) reducing electric cooling fan size, e.g., by reduced fan motor power;

3) for hybrid and fuel cell vehicles the possibilities also include:

-   -   3a) reducing power electronics radiator size, e.g., by core        thickness reduction, fin density reduction, and/or by reducing        core face area reduction, and/or    -   3b) reducing electric motor cooler size, e.g., by reduced core        thickness, fin density reduction, and/or core face area        reduction.

In another aspect, there is a reduction of mass and cost of propulsioncooling systems for the following vehicles: hybrid vehicles that haveeither an electric A/C compressor or an external capacity control A/Ccompressor; fuel cell vehicles that have either an electric A/Ccompressor or an external capacity control A/C compressor; andconventional power train vehicles that have an external capacity controlA/C compressor; as well as conventional power train vehicles that have afixed displacement A/C compressor.

In a further aspect, the realization of cabin air conditioning ismaintained during propulsion system thermal excursions and improved fueleconomy is realized due to, for example, reduced CRFM (CondenserRadiator Fan Module) electric fan power and CRFM mass.

BRIEF DESCRIPTION OF THE DRAWINGS

Various other features and attendant advantages of the present inventionwill be more fully appreciated as the same becomes better understoodwhen considered in conjunction with the accompanying drawings, in whichlike reference characters designate the same or similar parts throughoutthe several views, and wherein:

FIG. 1 is a perspective view of a controller according to the inventionin combination with an automotive vehicle, wherein in the illustratedexample the vehicle is a hybrid vehicle;

FIG. 2 is a flow chart outlining operation of the controller of FIG. 1;

FIG. 3 is a diagrammatical illustration of the controller used with astrong-hybrid arrangement;

FIG. 4 is a diagram illustrating results for a specific simulation in ahybrid or non-hybrid vehicle;

FIG. 5 is a graph of theoretical eThermal simulation results for an A/Csystem optimization of a propulsion cooling system of reduced size in anon-hybrid vehicle;

FIG. 6 is a graph of eThermal simulation results for a model of an A/Csystem optimization in a propulsion cooling system of reduced size usedin a non-hybrid vehicle;

FIG. 7 is a tabulation of results for examples of amounts of condenserheat load reduction showing positive impacts to the vehicles, and

FIG. 8 is a graph of eThermal simulation results for an A/C systemoptimization of reduced propulsion cooling system size in a non-hybridexample.

DETAILED DESCRIPTION

Referring now to FIG. 1, a controller 10 in a hybrid vehicle 11selectively connects an IC engine 13 or an electric traction motor 14 tothe drive wheels 15 of the hybrid vehicle. The controller 10 is mountedat any convenient location in the vehicle 11, but typically is mountedin an engine compartment 16. Controllers such as cabin temperaturecontrollers and controllers for HVAC systems including a compressor 17and a condenser 18 are preferably installed in the cabin, for example,within the instrument panel, or under the seats, or maybe installed inthe trunk.

FIG. 2 is a flow chart outlining the step-by-step operation of acontroller 10 according to the invention. In the “initial step,” thecontroller 10 checks a first truth table 21 to determine if any of thefollowing conditions are true:

-   -   1) whether the operating temperature of the engine coolant is        higher than a temperature limit T1A and lower than a temperature        limit T2A, or    -   2) whether the operating temperature of the transmission oil is        higher than a temperature limit T1B and lower than a temperature        limit T2B, or    -   3) whether the operating temperature of the inverter coolant is        higher than a temperature limit T1C and lower than a temperature        limit T2C, or    -   4) whether the operating temperature of the electric motor is        higher than a temperature limit T1D and lower than a temperature        limit T2D.

Information on various other parameters applicable to a given system mayalso be checked by the controller in its decision making process. Thetemperature limits T1A, T2A, T1B, T2B, T1C, T2C, T1D and T2D, arepredetermined based on design choices for a given vehicle 12.Temperature limits T1C, T2C, T1D and T2D apply only to hybrid and fuelcell vehicles.

If the answer to all of the parameters checked in the initial step bythe truth table 21 is “YES,” then the A/C system operation is withinnormal ranges and the controller 10 periodically repeats the sameinitial step of checking the parameters.

If the answer to any of the parameters in the initial step 21 is “NO,”then the controller 10 responds in step 22 by:

1) increasing cabin recirculation of air by X %,

2) reducing cabin blower speed by Y %, and/or

3) reducing compressor capacity by Z %.

These adjustments achieve a reduction of A/C condenser heat load.Preferably, all three, i.e., increasing cabin recirculation of air by X%, reducing cabin blower speed Y %, and reducing compressor capacity Z %are performed to achieve optimization according to the invention.Alternatively, any one or more, or preferably two of the threeprocedures in step 22 are performed. The percent values for X, Y, Z arepredetermined based on design choices for a given vehicle 12.Alternatively, the X, Y, Z values are based on a calculation in thecontroller 10 based on various data, such as vehicle operatingparameters/conditions.

Following the above steps 21 and 22 which achieve a reduction of A/Ccondenser heat load, the controller 10 checks a second truth table 23 todetermine whether any of the following conditions are true:

1) the operating temperature of the engine coolant is higher than thehigh temperature limit T2A, or2) the operating temperature of the transmission oil is higher than thehigh temperature limit T2B, or3) the operating temperature of the inverter coolant is higher than thehigh temperature limit T2C, or4) the operating temperature of the electric motor is higher than thehigh temperature limit T2D.The controller 10 may also check information on various other parametersnot in the illustrated truth table 23 applicable to a given system. Thevalues the high temperature limits T2A-T2D can be the same as thetemperature limits in pre-corresponding order listed in the initial step21 of the controller 10, or alternatively the values can be different.For example, the temperature values of the first predetermined valuesT2A-T2D, other than the values in the first step 21, can be a functionof the temperature values of the first step.

If the answer to any of the parameters is “YES in the second truth table23, the A/C compressor is shut off and a Flag AA is set in step 24. Thenthe controller 10 repeats checking the parameters discussed above. Ifthe answer to all of the parameters that have been checked is “NO,” thenthe controller 10 checks as to whether Flag AA in an A/C restart mode.

If the Flag AA is present, the A/C system is restarted by the A/Crestart step 24 to perform cabin recirculation at limited cabin blowerspeed and reduced compressor capacity. Preferably, all three, i.e.,cabin recirculation plus limited cabin blower speed and reducedcompressor capacity are performed to achieve optimization according tothe invention. Alternatively, any one or more preferably two of thethree may be performed. The cabin recirculation, limited cabin blowerspeed and reduced compressor capacity is limited and/or reduced bypredetermined amounts, or alternatively are a function of full capacityvalues, e.g., a percentage of the same or are based on various changingvehicle performance parameters/conditions, for example, a calculationbased on data provided to the controller 10. Following the check of theFlag AA 25, the controller 10 rechecks the truth table 21.

FIG. 3 depicts a hybrid air conditioning system, in which an air stream30 enters the system from the front end of the vehicle 12 and passesthrough an A/C condenser 31. Downstream of the A/C condenser 31, the airstream 30 passes through a transmission oil cooler 32 and a powerelectronics heat exchanger 33. Transmission oil 35 circulates betweenthe transmission oil cooler 32 and transmission 36. Fluid 39 circulatesfrom the power electronics heat exchanger 33 to a power train powerelectronics and/or electric traction motor 40 followed by vehicle powerelectronics 41. Further downstream, the air stream 30 passes through anengine radiator 43 positioned in front of an electric fan package 44,which engine radiator cools coolant fluid from the IC engine 13 of FIG.1.

FIG. 4 illustrates a hybrid simulation in which the air conditioningload is decreased according to the previously discussed arrangementillustrated in FIG. 2. In FIG. 4, there is heat rejection in front ofthe engine radiator 43 due to the conditioned air 30 passing throughboth the auxiliary transmission oil cooler 32 and the AC condenser 31.When the load on the AC condenser 31 is reduced using the method of FIG.2, there is a reduction of less than 10% in the air available to coolcoolant in the engine radiator 43 due to heat rejection by both the ACcondenser 31 and the auxiliary transmission oil cooler 32. This resultsin approximately 10% reduction in the temperature of the coolant fromthe internal combustion engine 13 (FIG. 1) to the engine radiator 43,which reduces power train cooling content, i.e., the mass, dimensionsand thus cost of the heat exchanger (the engine radiator 43) and thecooling fan package 44 (FIG. 2). This feature is available for bothhybrid and non-hybrid vehicles as well as fuel cell vehicles in whichthe internal combustion engine 13 is replaced by a fuel cell.

FIG. 5 is a graph of results using data for an A/C system optimizationfor a propulsion cooling system of reduced size in a non-hybrid vehicle.Conditioned air results in KW and Temperature T (C) are graphed as afunction of time and include condenser outside air (OSA) 51 introducedinto the cabin; condenser recirculated air 52; condenser air outtemperature 53; conditioner recirculated air out temperature 54 andengine rpm/100 55. As is seen in FIG. 5, by using the method of FIG. 2,there is an approximately 50% reduction in conditioner heat load 51 fromheat load of the cabin OSA 51 compared with the heat load of cabinrecirculation air 52. There is also about a 10% reduction in conditionerair out temperature 54 when using the method of FIG. 2.

FIG. 6 is a graph similar to FIG. 5, but also plotting the temperature57 of coolant into the engine radiator 43 during cooling of outside air,as well as the temperature 59 of coolant into the engine radiator 43during cooling of recirculating air from the cabin of the vehicle. It isseen from FIG. 6 that by employing the method of FIG. 2, wherein cabinrecirculation air is increased, while cabin blower speed and compressorcapacity are reduced during recirculation, the temperature 59 of coolantinto the engine radiator 43 is substantially lower than the temperature57 of coolant into the engine radiator when outside air is being cooled.This difference allows for a smaller radiator size, as well as fanpackage size in non-hybrid vehicles. In hybrid or fuel cell poweredvehicles, condensers run by electric motors consume less power byincreasing cabin recirculation while reducing cabin blower speed andcompressor capacity.

FIG. 7 is a chart tabulating examples of condenser heat load reductionresulting improvements to the vehicle efficiency. The chart shows thatfor hybrid/fuel cell vehicles with electric A/C compressor, the averageA/C condenser heat load reduction by forcing cabin recirculation andhaving reduced compressor capacity is about 11%, which impacts thevehicle by a reduction in transmission sump temperature and a reductionin engine radiator inlet coolant temperature.

For non-hybrid vehicles with a belt driven compressor, where cycling isfixed if using a displacement compressor, displacement can be reduced ifusing a variable capacity compressor. There are also improvements inefficiency. As is set forth in the chart of FIG. 7, the average A/Ccondenser heat load reduction by forcing cabin recirculation and havingreduced compressor capacity is about 50%. This results in a reduction inengine radiator inlet coolant temperature or a reduction in EngineRadiator Core Thickness. This provides a potential production costoption in designing and/or manufacturing an automotive vehicle.

FIG. 8 illustrates results in a graph for an A/C system optimization forreduced propulsion cooling system size in a non-hybrid example.Condenser heat load 81 in watts (w) and engine rpm 82, as well asvehicle speed 83 in kph and condenser air out temperature 84 in ° C. areplotted as a function of time with cabin HVAC in a recirculation mode 92versus an outside air (OSA) mode 94 with the vehicle on 0% grade. Thedata shows that when the system is in a cabin recirculation mode, thecondenser load 92 is lower than when the system is in cabin in OSA mode94. The method of FIG. 8 is carried out by a controller operated inaccordance with the method of FIG. 2. While the data plotted is for anon-hybrid vehicle, the same principles apply for hybrid and fuel cellvehicles.

From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention, and withoutdeparting form the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions.

1) A method of optimizing an air conditioning system control in avehicle comprising momentarily reducing air conditioner condenser heatload via electric compressor speed control, forced cabin recirculation,and/or reduced cabin blower speed during transient, high ambient andhigh propulsion system load events. 2) A method according to claim 1,wherein all three of electric compressor speed control, forced cabinrecirculation, and reduced cabin blower speed are performed. 3) A methodof optimizing an air conditioning system control in an air conditioningsystem for a vehicle, comprising the steps of: I) checking: 1) whetherthe temperature of the engine coolant is higher than a first enginecoolant temperature limit and lower than a second engine coolanttemperature limit, 2) whether the temperature of the transmission oil ishigher than a first transmission oil temperature limit and lower than asecond transmission oil temperature limit, Ia) if the answer to 1 or 2is yes, then repeating I), Ib) if the answer to 1 or 2 is no, thenproceeding to step II), II) reducing air conditioner heat load by: 1)increasing cabin recirculation of air 2) reducing cabin blower speed 3)reducing air conditioner compression III) after step II), checking 1)whether the engine coolant temperature is higher than the second enginecoolant temperature limit; and 2) whether the transmission oiltemperature of the transmission oil is higher than the secondtemperature limit; IIIa) if the answer to 1 or 2 is yes, then shuttingoff the A/C compressor, setting a flag and then repeating step III),IIIb) if the answer is no, then checking for the presence of the flag,IIIbi) if the flag is present, performing cabin recirculation, limitingcabin blower speed and reducing compressor capacity followed byrepeating step I), IIIbii) if no flag is present, repeating step I). 4)The method according to claim 3, wherein the temperature limits arepredetermined values. 5) The method according to claim 3, wherein instep II) cabin recirculation of air is increased by X %, cabin blowerspeed is increased by Y %, and compressor capacity is reduced by Z %. 6)The method according to claim 3, wherein X, Y and Z are predeterminedvalues. 7) The method according to claim 3, wherein X, Y and Z arecalculated values. 8) A method of designing vehicles comprisingdetermining propulsion cooling system size which achieves predeterminedperformance while performing the method according to claim
 3. 9) Themethod according to claim 8, wherein the cooling system size is reducedfrom a size the cooling system would have been without the vehiclesperforming a method according to claim 3 while having the samepredetermined performance, comprising: reducing radiator cooling size bycore thickness reduction, fin density reduction, or core face areareduction; and reducing fan motor power. 10) A method of optimizing anair conditioning system control in an air conditioning system for ahybrid or fuel cell vehicle, comprising the steps of: I) checking: 1)whether the temperature of the engine coolant is higher than a firstengine coolant temperature limit and lower than a second engine coolanttemperature limit, 2) whether the temperature of the transmission oil ishigher than a first transmission oil temperature limit and lower than asecond transmission oil temperature limit, 3) whether the temperature ofthe inverter coolant is higher than a first inverter coolant temperaturelimit and lower than a second electric motor temperature limit, and 4)whether the temperature of the electric motor is higher than a firstelectric motor temperature limit and lower than a second electric motortemperature limit, Ia) if the answer to all of 1), 2) 3) and 4) checkedis yes, then repeating I), Ib) if the answer to any of 1), 2) 3) or 4)is no, then proceeding to step II), II) reducing air conditioner heatload by: 1) increasing cabin recirculation of air, or 2) reducing cabinblower speed, or 3) reducing air conditioner compressor capacity, III)after step II), checking 1) whether the engine coolant temperature ishigher than the second engine coolant temperature limit; 2) whether thetransmission oil temperature of the transmission oil is higher than thesecond temperature limit; 3) whether the inverter coolant temperature ofthe inverter coolant is higher than the second inverter coolanttemperature limit; 4) whether the electric motor temperature of theelectric motor is higher than the second electric motor temperaturelimit; IIIa) if the answer to any of 1), 2) 3) or 4) is yes, thenshutting off the A/C compressor, setting a flag and then repeating stepII), IIIb) if the answer to all of the parameters that have been checkedis no, then checking for the presence of the flag, IIIbi) if the flag ispresent, performing cabin recirculation, limiting cabin blower speed andreducing compressor capacity followed by repeating step I), IIIbii) ifno flag is present, repeating step I). 11) The method according to claim3, wherein the temperature limits are predetermined values. 12) Themethod according to claim 3, wherein the temperature limits arecalculated values. 13) A method of designing vehicles comprisingdetermining propulsion cooling system size which achieves predeterminedperformance while performing the method according to claim
 10. 14) Themethod according to claim 13, wherein the cooling system size is reducedfrom a size having the same predetermined performance, comprising:reducing radiator cooling size by core thickness reduction, fin densityreduction, or core face area reduction; and reducing fan motor power.15) The method of claim 14 wherein the vehicle is a hybrid or fuel cellvehicle and the method further comprises: reducing power electronicsradiator size by core thickness reduction, fin density reduction, andcore face area reduction, and reducing electric motor cooler size byreduced core thickness, fin density reduction, and core face areareduction. 16) A method of optimizing an air conditioning system controlfor an air conditioning system having a compressor in hybrid or fuelcell having an electric drive motor, the method comprising: determiningthe operating temperature of at least one of the following vehiclecomponents: engine coolant, transmission oil, inverter coolant and theelectric drive motor; comparing the at least one operating temperatureto lower and upper temperature limits; if the operating temperature isoutside of the temperature limits reducing air conditioner heat load byat least one fo the following steps: increasing cabin air recirculation,reducing cabin blower speed and reducing air conditioner compressorcapacity; subsequent to reducing air conditioner heat load, monitoringthe operating temperature to determine if the operating temperatureexceeds the upper temperature limit, shutting off the compressor if theoperating temperature exceeds the upper limit; repeating the step ofdetermining the operating temperature, and restarting the compressoronce the operating temperature is below the upper temperature limit torecirculate conditioned air a limited blower speed on reduced compressorcapacity. 17) The method of claim 16 wherein the operating temperaturesof at least two of the vehicular components are determined. 18) Themethod of claim 16 wherein the operating temperatures of three of thevehicular, components are determined. 19) The method of claim 16 whereinthe operating temperatures of four of the vehicular components aredetermined.